ingest: document fields that support templating (#34536)
ingest: document fields that support templating (#34536)

This change also updates many of the examples to use ecs as the example.
Some additional minor improvements are also included.

Part of #33188

vroyer/elassandra,strapdata/elassandra,strapdata/elassandra,vroyer/elassandra,strapdata/elassandra,strapdata/elassandra,strapdata/elassandra,vroyer/elassandra